This invention relates generally to an electrophotographic printing machine and, more specifically, to a document handling system which includes a grooved vacuum belt for transporting original documents to an exposure station.
For the higher speed electrophotographic printing machines now in commercial use, it is increasingly desirable to provide for the automatic handling of individual original documents being copied in order to utilize these copiers to the fullest extent. However, the characteristics of the original documents can vary widely, i.e. in size, weight, thickness, material, condition, humidity, age, etc. These documents may have curls, wrinkles, tears, cutouts, overlays, paste ups, tapes, staples, abrasive areas or other irregularities. Under all of these conditions it is desirable to be able to semi-automatically or automatically copy a set of such documents. Presently, there are various types of document handling systems which move original documents over the platen. These may be made from single or multiple belts which utilize vacuum retaining forces to secure the document against the belt.
Generally, the belt has vacuum apertures extending through the belt which cooperate with the vacuum-producing means to create a suctional force against documents fed between the belt and a document platen. One problem with apertured document handlers is that, when light weight documents are being copied (e.g. 9-13 pound range), the apertures create a high density differential relative to the belt with the result that output copy has undesirable background spots or shadows corresponding to the aperture areas. Various expedients to minimizing this background problem have been disclosed in prior publications, for example, U.S. Pat. No. 3,677,643 (Sagana), U.S. Pat. No. 4,047,812 (Hogan), and U.S. Pat. No. 3,963,345 (Stemmle). In these prior art systems, the document handler belt is reflective and the plenum areas adjacent (and above) the apertured area are made reflective in order to back illuminate the aperture thereby reducing the density differential. These techniques have not, however, been completely successful.
A second background minimization technique is to utilize a translucent, document belt in combination with a reflective grooved channel adjacent the belt apertures as disclosed in copending U.S. patent application Ser. No. 191,560 filed Sept. 29, 1980. While this technique satisfactorily resolves the aperture show-through problem, the transparent/translucent belt is susceptible to contamination at the plenum/belt interface. Thus dirt, scratches, etc. on the belt surface will print out as undesirable background on output copy.
In accordance with the present invention there is provided a document handling system of the type in which a document is transported to an imaging station of an electrophotographic printing machine comprising:
at least one document transport belt having a plurality of apertures therethrough, said belt having a reflective surface except for areas surrounding said apertures, said areas being at least partially transmissive to light, and
vacuum means in communication with said belt for retaining the document therein, said means having reflective areas in optical communication with said belt aperture areas.